.ABSTRACT The Arizona Department of Education (ADE) empowered a task force to design a new instructional model for English Language Development (ELD) students. The task force created a four-hour, language intensive instructional model which required ELD-indentified students to be immersed in grammar, reading, pre-writing, vocabulary and oral English conversation. This model also mandated a specific number of instructional minutes were to be assigned to each of the model's five components. Moreover, these instructional minutes were to be accounted for by ELD teachers as they developed lesson plans to teach these students. To address the substantial professional development requirements entailed by these mandates, Wenger's Community of Practice (CoP) framework was employed. A CoP was formed to assist nine ELD teachers to (a) meet mandates of the instructional model, (b) participate in professional development opportunities to gain language-based instructional strategies, (c) plan lessons together and eventually, (d) allow them to become more efficacious in their abilities to meet and implement the mandated ADE Sheltered English Instruction (SEI) instructional model developed by the ADE task force. Quantitative and qualitative data were gathered throughout the study by means of a pre- and post-questionnaire, audio taping and transcribing CoP sessions and field notes. Findings suggest the CoP served as an effective forum for increasing ELD teachers' sense of efficacy towards becoming an effective ELD teacher. Moreover, the CoP helped increase understanding of the requirements of the instructional model, participate in professional development specific to their needs and collaborate, which was largely responsible for increasing teacher efficacy.